Additive Manufacturing or 3D printing of ceramics or ceramic composites is in its infancy. Due to the high temperature requirements and the difficulties of using bulk ceramic precursors, additive manufacturing of ceramics is not as well developed as the 3D printing of metals and polymers which are easier to cast, mold or machine into various shapes and sizes.
The issues with Polymer Derived Ceramics have historically been that “the polymer to ceramic conversion occurs with gas release which typically leads to cracks or pores which make the direct conversion of a preceramic part to dense ceramic virtually unachievable unless its dimension is typically below a few hundred micrometers (as in the case of fibers, coatings, or foams.) J. Am. Ceram. Soc. 93 [7] p. 1811 (2010). Commonly owned, U.S. Pat. No. 8,961,840 is incorporated herein by reference, is related to the present invention and solves the problem of making a direct conversion of a preceramic part (green body) to a dense, monolithic ceramic without cracks or pores traditionally caused by gas release during pyrolysis.
There are a couple of techniques that are currently used in commercial applications. One is the technique used by Robocasting Enterprises where a ceramic slurry is squeezed out of an applicator similar to the application of toothpaste to a toothbrush. The deposition pattern is controlled by a 3D CAD file to produce an initial green body which then must be heat treated at very high temperatures to densify to the final ceramic. Ceramics made with the robocasting technique include traditional ceramics such as alumina, zirconia, silicon nitride, and silicon carbide.
Another technology is one that is represented by 3DCeram where high viscosity, ultra violet (UV) light curable materials, in paste form are used. These photocurable resin compounds containing ceramic powders are laid down in a manner such that a laser that is controlled by a 3D CAD file can polymerize the pastes. Then, another ceramic-UV curable paste layer is laid down on top of the previous layer followed by another laser treatment controlled by the 3D CAD file. This process is repeated until the final 3D shape is obtained. The parts are then heat treated for the purpose of debinding the photocurable resin and then sintering the ceramic particles in order to eliminate the resin and densify the ceramic. Again, extreme temperatures in excess of 1600° C. for long intervals are required to sinter the ceramics together. This high temperature process is very energy intensive, thus very expensive, and limits the composites that can be made with these techniques due to the temperatures required to sinter ceramics being generally higher than the melting temperature of most metals.
A recent advancement in additive manufacturing or 3D printing of ceramics or ceramic composites is reported by Zak E. Eckel et al. in Science, “Additive manufacturing of polymer-derived ceramics,” 1 Jan. 2016, Vol. 351, Issue 6268, sciencemag.org with Supplementary Materials at www.sciencemag.org/content/351/6268/58/suppl/DC1. Eckel et al. teach the fabrication of fully dense ceramic structures with no porosity or surface cracks in intricate shapes, such as, rib, corkscrew, lattice and honeycomb, using ultraviolet (UV) light curable liquid polymer resins, exposing the liquid resin to UV light through a patterned mask using self-propagating photopolymer wave-guide technology (SPPW) to rapidly create structures 100 to 1000 times more rapidly than with traditional layering. The architecture of the structure is defined by a patterned mask that defines the areas exposed to a collimated UV light source. To avoid shattering on pyrolysis, the printed polymer structure is typically limited to fine features with less than approximately 3 mm in thickness in one dimension. The size limitations of the structure are a drawback.
Thus, another additive manufacturing/3D printing technique is needed to create solid, monolithic, bulk ceramic composite structures for aerospace, propulsion and other high performance applications. Polymer Derived Ceramics (PDCs) of the present invention provide highly desirable bulk ceramic and ceramic composites in much lower temperature ranges without the need for sintering of previously made ceramic particles.